A generator system for a gas turbine engine, such as that found in aircraft, ships, and some terrestrial vehicles, may include three separate brushless generators, namely, a permanent magnet generator (PMG), an exciter, and a main generator. The PMG includes permanent magnets on its rotor. When the PMG rotates, AC currents are induced in stator windings of the PMG. These AC currents are typically fed to a regulator or a generator control device, which in turn outputs a DC current. This DC current next is provided to stator windings of the exciter. As the rotor of the exciter rotates, three phases of AC current are typically induced in the rotor windings. Rectifier circuits that rotate with the rotor of the exciter rectify this three-phase AC current, and the resulting DC currents are provided to the rotor windings of the main generator. Finally, as the rotor of the main generator rotates, three phases of AC current are typically induced in its stator, and this three-phase AC output can then be provided to a load such as, for example, an aircraft, ship, or vehicle electrical system.
Because some generator applications are high speed generators with potential rotational speeds up to and in excess of 24,000 rpm, potentially large centrifugal forces may be imposed upon the rotors in generators. Given these potentially stressful operating conditions, the rotors should be carefully designed and manufactured, so that the rotors are reliable and precisely balanced. Improper balancing not only can result in inefficiencies in the operation of a generator, but may also affect the reliability of the generator.
Rotor imbalance may be alleviated by using any one of several techniques. For example, the rotor may undergo a grinding process to remove material. However, typically, several attempts are needed to remove a sufficient amount of material from appropriate sections of the rotor. Additionally, debris from the grinding process may undesirably remain in the rotor and thereby cause the rotor to function improperly. In other examples, imbalance is corrected by adding material to the rotor. In most conventional rotor configurations, axial openings are formed through a portion of an outer periphery of a rotor armature and at each end of the rotor. One or more masses are then inserted into the axial openings. However, because the axial openings are only formed in the outer periphery and at the rotor ends, balance correction is limited to certain planes.
Hence, there is a need for a system and method for correcting imbalance in the rotors of a high speed generator by increasing the number of planes, throughout the length of the rotor, at which balance weights can be introduced. The present invention addresses one or more of these needs.